A high-voltage power supply may be provided in vehicles, such as electric vehicles. Conventionally, a ground fault between the high-voltage part of a vehicle (high-voltage side) and the vehicle body has been detected. In the case of a ground fault, the potential of the vehicle body (body earth) is unstable and may affect operations by the low-voltage part of the vehicle (low-voltage side).
JP 2003-250201 A (PTL 1), for example, discloses a method to detect a ground fault by applying a pulse voltage via a resistor to a capacitor having one terminal connected to the high-voltage side and monitoring the voltage waveform at the connection point between the capacitor and the resistor. The method in PTL 1 reduces the effect of impedance caused by the capacitance of the vehicle body itself and allows highly accurate detection of a ground fault.